1. Field of the Invention
The present invention relates to an apparatus for iteratively measuring a value of a periodic physical information including a periodically changing component and removing one or more abnormal values from the iteratively measured values of the periodic physical information.
2. Discussion of Related Art
When a sort of physical information is obtained or measured from a patient, for the purpose of diagnosing a disease of the patient or monitoring a physical condition of the patient, the physical information is often measured continuously to improve the accuracy of measurement or find any significant change of the information during the measurement.
For example, a degree of arteriosclerosis may be diagnosed based on a pulse-wave propagation velocity at which a pulse wave propagates through an artery of a patient. The measurement of pulse-wave propagation velocity needs to measure a pulse-wave propagation time needed for the pulse wave to propagate from a first portion, to a second portion, of the artery. To this end, a rising or start point of a second heart sound, II, detected by a heart-sound sensor from the heart of the patient may be used as a first or upstream-side point to measure the pulse-wave propagation time. Here, the accuracy of detection of the start point of the second heart sound II may be improved by detecting respective start points of a plurality of second heart sounds II and calculating an average of the detected start points. More specifically described, first, respective time durations from respective reference waves to respective start points of a plurality of second heart sounds II are measured, and then an average of those time durations is calculated. For example, the reference waves may be respective R waves of an electrocardiogram (ECG) whose waveform can be clearly detected. That is, respective time durations, R-II, from respective R waves of ECG waveform to respective start points of second heart sounds II are measured, and then an average of those time durations R-II is calculated. Thus, the measurement of pulse-wave propagation velocity may need to iteratively measure, in advance, the time durations R-II as a sort of physical information of the patient.
However, the second heart sounds II detected by the heart-sound sensor are easily mixed with noise. Therefore, the time durations R-II measured as described above may include one or more aberrant or abnormal values produced by the noise. In addition, not only the second heart sound II but also other sorts of physical information obtained from a living subject are easily mixed with noise. Thus, the measured values of each sort of physical information may include one or more abnormal values resulting from the occurrence of one or more errors during the measurement. In addition, there is a need to finish the measurement in a short time to reduce the burden exerted to the patient. To this end, the total number of measured values of the physical information should be as small as possible. However, if the small number of measured values include one abnormal value, it may adversely influence a diagnosis to be made for the patient.
Here, it is possible to make a graph showing a distribution of the measured values of physical information, judge one or more values largely deviated from the distribution, as being abnormal, and remove the values judged as abnormal.
However, there is known a periodic physical information having a periodically changing component. Even if the measured values of periodic physical information may include one or more abnormal values resulting from erroneous measurement, the abnormal value or values may not be largely deviated from the distribution of measured values and may not be Judged as being abnormal, or removed. FIGS. 10A and 10B show abnormal values which cannot be discriminated or removed. More specifically described, FIG. 10A shows a graph representing respective values of periodic physical information that are iteratively measured as time elapses. An axis of abscissa is indicative of the time, and an axis of ordinate is indicative of the magnitude or value of periodic physical information. Circles 80 indicate correctly measured values of periodic physical information, a cross 82 indicates an abnormal value resulting from erroneous measurement. A periodic curve, C, represents a waveform of the periodically changing component of the periodic physical information.
FIG. 10B shows a histogram representing the respective measured values of periodic physical information. The abnormal value indicated by the cross 82 in FIG. 10A is located at an outermost end of the distribution shown in FIG. 10B, but is not clearly deviated from the other measured values. Thus, it is difficult to find and discard the abnormal value 82. In addition, in FIG. 10A, a triangle 84 also indicates an abnormal value which, however, falls within the periodic change of the physical information. Since this abnormal value is mixed with the normal celio values in the histogram shown in FIG. 10B, it cannot be found or discarded. Thus, it has been difficult to discard one or more abnormal values from the measured values of any sort of periodic physical information.
It is therefore an object of the present invention to provide a periodic-physical-information measuring apparatus which iteratively measures a value of periodic physical information and which can easily remove one or move abnormal values from the iteratively measured values of periodic physical information.
The present invention provides a periodic-physical-information measuring apparatus which has one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (6). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature.
However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited.
(1) According to a first feature of the present invention, there is provided an apparatus for measuring a periodic physical information of a living subject, comprising a measuring device which iteratively measures, from the subject, a value of the periodic physical information comprising a periodically changing component; a waveform determining means for determining a changing-component waveform representing the periodically changing component of the periodic physical information; a difference determining means for determining at least one difference between at least one first value of the periodic physical information measured by the measuring device at at least one time and at least one second value of the changing-component waveform at the at least one time; and a removing means for judging, based on the at least one difference determined by the difference determining means, whether the at least one first value is abnormal, and removing the at least one first value judged as being abnormal.
In the present periodic-physical-information measuring apparatus, the measuring device measures values of the periodic physical information, the waveform determining means determines the changing-component waveform representing the periodically changing component of the periodic physical information measured by the measuring device, the difference determining means determines a difference between a first value of the periodic physical information measured by the measuring device at a time and a second value of the changing-component waveform at that time, and the removing means judges, based on the determined difference, whether the first value is abnormal, and removes the first value of the periodic physical information that is judged as being abnormal. Thus, the present apparatus can easily remove one or more abnormal values from the iteratively measured values of periodic physical information.
(2) According to a second feature of the present invention that includes the first feature (1), the measuring apparatus further comprises an average determining means for determining an average of the iteratively measured values of the periodic physical information from which the at least one first value judged as being abnormal has been removed. In the present measuring apparatus, the average determining means determines an average of the iteratively measured values of the periodic physical information from which the one or more first values judged as being abnormal has or have been removed. This average is more accurate than an average of the values of periodic physical information from which no abnormal values have been removed.
(3) According to a third feature of the present invention, there is provided an apparatus for measuring a periodic physical information of a living subject, comprising a measuring device which iteratively measures, from the subject, a value of the periodic physical information comprising a periodically changing component resulting from a respiration of the subject; a respiration-wave detecting device which detects a respiration wave resulting from the respiration of the subject; a waveform determining means for determining, based on the respiration wave detected by the respiration-wave detecting device, a changing-component waveform representing the periodically changing component of the periodic physical information; a difference determining means for determining at least one difference between at least one first value of the periodic physical information measured by the measuring device at at least one time and at least one second value of the changing-component waveform at the at least one time; and a removing means for judging, based on the at least one difference determined by the difference determining means, whether the at least one first value is abnormal, and removing the at least one first value judged as being abnormal.
In the present periodic-physical-information measuring apparatus, the measuring device measures respective values of the periodic physical information containing the periodically changing component resulting from the respiration of the subject, the respiration-wave detecting device detects the respiration wave resulting from the respiration of the subject, the waveform determining means determines, based on the respiration wave, the changing-component waveform representing the periodically changing component of the periodic physical information, the determining means determining a difference between a first value of the periodic physical information measured at a time and a second value of the changing-component waveform at that time, and the removing means judges, based on the determined difference, whether the first value is abnormal, and removes the first value of the periodic physical information that is judged as being abnormal. Thus, the present apparatus can easily remove one or more abnormal values from the iteratively measured values of periodic physical information containing the periodically changing component resulting from the respiration of the subject.
(4) According to a fourth feature of the present invention that includes the third feature (3), the measuring apparatus further comprises an average determining means for determining an average of the iteratively measured values of the periodic physical information from which the at least one first value judged as being abnormal has been removed. In the present measuring apparatus, the average determining means determines an average of the iteratively measured values of the periodic physical information from which the one or more values judged as being abnormal has or have been removed. This average is more accurate than an average of the iteratively measured values of periodic physical information from which no abnormal values have been removed.
(5) According to a fifth feature of the present invention that includes the third or fourth features (3) or (4), the respiration-wave detecting device comprises a chest-impedance-pulse-wave detecting device which detects a chest-impedance pulse wave from a chest of the subject; and an extracting means for extracting the respiration wave from the chest-impedance pulse wave detected by the chest-impedance-pulse-wave detecting device. Since the chest-impedance pulse wave detected by the chest-impedance-pulse-wave detecting device contains a respiration-synchronous component, the extracting means extracts, as an accurate respiration wave, the respiration-synchronous component from the chest-impedance pulse wave.
(6) According to a sixth feature of the present invention that includes any one of the third to fifth features (3) to (5), the measuring device comprises an electrocardiograph device which includes a plurality of electrodes adapted to be placed on a plurality of body portions of the subject, continuously detects an electrocardiogram waveform, from the subject through the electrodes, and outputs an electrocardiogram-waveform signal representing the detected electrocardiogram waveform; a heart-sound sensor which detects a plurality of second heart sounds, II, produced from the heart of the subject, and outputs a heart-sound signal representing the detected second heart sounds II; and a measuring means for iteratively measuring a time difference between a first time when a predetermined periodic point on the electrocardiogram waveform is detected by the electrocardiograph device and a second time when a start point of each of the second heart sounds II is detected by the heart-sound sensor. In the case where the above-described average determining means determines an average of the iteratively measured time differences from which one or more abnormal time differences have been removed, the thus determined average is more accurate than an average of the iteratively measured time differences from which no abnormal time differences have been removed. In addition, since the electrocardiogram waveform is not easily mixed with noise and accordingly is accurately detected, the average of the time differences measured based on the electrocardiogram waveform provides an accurate time when the second heart sound II occurs as measured from the predetermined periodic point on the electrocardiogram waveform